1. Field of the Invention
The present invention relates generally to fluid pumps, and more particularly to miniature jack or piston pumps.
2. Related Art
Miniature pumps have been used in a variety of applications such as drug delivery devices, miniature hydraulic systems, and the like. Some miniature pumps flex a diaphragm or use a dragging seal to create a vacuum to move fluid into and out of the pump. Other miniature pumps, such as piston pumps, have to rotate or slide a seal in order to push or impel fluid through the pump. The moving seals in these types of pumps have presented problems in that relatively significant amounts of power are needed in order to overcome resistive frictional forces and move the seals. Consequently, relatively large batteries or other power sources have been required to power these miniature pumps, thereby reducing the size benefit of the miniature pump.
Additionally, very small pumps typically operate at relatively high frequencies. The rapid cycling of pistons, impellors, and seals can wear the seals and cause leakage of the pumped fluid out of the pump. Moreover, high frequency cycling can cause cavitation, or the generation of gas bubbles, within the fluid flow path in the pump. Bubbles in the fluid stream affect the output volume of the pump and affect pump efficiency. Bubbles can also be dangerous to patients when such pumps are used as drug delivery devices.
Such small pumps are often used in applications that may require anti-back flow or anti-free flow measures, such as drug delivery systems. Unfortunately, anti-back flow or anti-free flow valves typically require additional bulky structure coupled to the pump outlet. These types of valves will sometimes limit the size of the reservoir or battery since the size of the overall system is often constrained by the space available for installation of the pump, such as a patient's abdominal cavity in the case of a sub-dermal drug pump.